Specific heat of pure graphite in the ultra-quantum limit region

We calculate the electronic specific heat of pure graphite in the ultraquantum limit region for fields between 60 and 200 kG, at very low temperatures, using the Slonczewski-Weiss band model with values of the energy-band parameters which are in agreement with recent magneto-replection experiments. The effect of trigonal warping of the Fermi surfaces associated with the parameter γ₃ is neglected in the calculation. Our results show that, for most of the range of fields considered, the electronic specific heat C is very nearly proportional to both the magnetic field strength H and the temperature T, according to the relation C ≈ αHT with a coefficient α of about 0.091 μJ/g-at. K²kG. The results also indicate that, at the upper end of the magnetic field range, the C(H) curves, at a given T, depart slightly and progressively from linearity with increasing H, essentially as a result of the variation of the Fermi energy with magnetic field.     

Specific heat of the Ca-intercalated graphite superconductor CaC6

The superconducting state of Ca-intercalated graphite CaC6 has been investigated by specific heat measurements. The characteristic anomaly at the superconducting transition (Tc = 11.4 K) indicates clearly the bulk nature of the superconductivity. The temperature and magnetic field dependence of the electronic specific heat are consistent with a fully gapped superconducting order parameter. The estimated electron-phonon coupling constant is lambda = 0.70 +/- 0.04, suggesting that the relatively high Tc of CaC6 can be explained within the intermediate coupling BCS approach.     

Specific heat of solid deuterium in the region of the proposed rotational glass phase

The specific heat of solid deuterium of 33% paradeuterium concentration has been measured for 1 K > T > 0.115K by a thermal relaxation technique. No evidence of a phase transition was found in the samples in the temperature range associated with the molecular rotational glass phase. No thermal remanence effects were observed for characteristic measurements times greater than 30 seconds. Integration of the specific heat indicates that rotational entropy of the solid below 0.35 Kelvin equals about 10% of the free rotator entropy, in agreement with ?P/?T)_V studies of solid H₂.     

Reentrant metallic behavior of graphite in the quantum limit

Magnetotransport measurements performed on several well-characterized highly oriented pyrolitic graphite and single crystalline Kish graphite samples reveal a reentrant metallic behavior in the basal-plane resistance at high magnetic fields, when only the lowest Landau levels are occupied. The results suggest that the quantum Hall effect and Landau-level-quantization-induced superconducting correlations are relevant to understand the metalliclike state(s) in graphite in the quantum limit.     

Specific heat in superconductors

Specific heat is a powerful tool to investigate the physical properties of condensed materials. Superconducting state is achieved through the condensation of paired electrons, namely, the Cooper pairs. The condensed Cooper pairs have lower entropy compared with that of electrons in normal metal, thus specific heat is very useful in detecting the low lying quasiparticle excitations of the superconducting condensate and the pairing symmetry of the superconducting gap. In this brief overview, we will give an introduction to the specific heat investigation of the physical properties of superconductors.We show the data obtained in cuprate and iron based superconductors to reveal the pairing symmetry of the order parameter.     

Specific heat of SbSI

The temperature dependence of the specific heat of vapor and flux grown single crystal samples of ferroelectric antimony sulfur iodide (SbSI) was measured over a temperature range from 230K to 400K. C_p^E at T_c of the electrical flux and vapor grown samples are 0.078 cal/gmK and 0.076 cal/gmK respectively. ΔS and ΔQ at T_c are evaluated. The samples measured were grown by two different methods[1,2]. Differences are observed between the measurements made on the samples, both in the magnitude of the specific heat and the temperature at which the ferroelectric transition takes place. These differences are caused by the different levels of oxygen impurities in the samples.     

Specific heats of pure and doped polyacetylene

The temperature dependences (0.8 K ? T < 7 K) of the specific heats of pure polyacetylene (both $\text{cis}$ and $\text{trans}$ isomers) and heavily doped metallic [CH(AsF₅)_0.12]_X are reported. Results for undoped $\text{cis}$-(CH)_X indicate behavior typical of crystalline polymers, whereas isomerization to the $\text{trans}$-form leads to a small term linear in temperature signifying increased disorder. Comparison of the data from $\text{cis}$ and $\text{trans}$ starting material indicates that isomerization is induced during doping. The increased coefficient of the linear term in the metallic polymer is discussed in terms of two contributions; an electronic term expected for a metal, and the increased effect of disorder in the doped polymer.     

Specific heat of the anisotropic rigid rotator

The exact (numerical) thermal evolution of the specific heatC of the single anisotropic (not necessarily equal inertial momentaI _x I _y I _xy andI ₂) quantum rigid rotator is calculated. For values ofI _xy /I _z low enough,C presents an unexpectedly high maximum; for sufficiently high values ofI _xy /I _z a second peak emerges. Also a quite rich T0 asymptotic behavior is exhibited.     

Low temperature magnetic susceptibility of pure graphite in strong magnetic fields

In this paper we present a calculation of the magnetic susceptibility of pure graphite for fields higher than 65kG so that at low temperatures, the only contribution to the susceptibility comes from the two ‘near’ n = 0 levels which intersect the Fermi surface. Under these conditions the susceptibility can be very different from its zero-field value and our results show that graphite which is strongly diamagnetic for low fields, becomes strongly paramagnetic at high fields.     

Specific heat studies of the spin-peierls transition

An experimental study is presented of the specific heat of the spin—Peierls systems TTF-TBT(M), M = Cu, Au. The linear term, γT, expected for the uniform one-dimensional antiferromagnet at low temperatures is observed above the Peierls transition. Specific heat anomalies associated with the transition are found at T_p(Cu) = 12.4K and T_p(Au) = 2.06K. The transition for TTF-BDT(Cu) is mean-field like; whereas the transition for TTF-BDT(Au) is broadened by one-dimensional fluctuation effects.     

Specific heat of around the glass transition

Dynamic calorimetric measurements are performed for the quaternary metallic glass Zr₆₅Al_7.5Cu_17.5Ni₁₀ in order to analyse the dependence on different heating rates for the glass transition temperature T_g. We compare two different temperature programs used for sample relaxation, to estimate the influence of the thermal history on T_g. A lower limit for the glass transition temperature T_g was calculated according to two different models based on the fact, that width and temperature of the glass transition depend on the experimental time scale set by the heating rate: One model assumes a Vogel-Fulcher-Tammann type behaviour, as used to describe more or less “fragile” glass formers and the other assumes an Arrhenius-like behaviour, which is related to “strong” glass formers. The values obtained from both models differ by about 80K. From additional absolute specific heat capacity measurements we calculate the Kauzmann temperature T_K, as a lower limit for the temperature of the glass transition from thermodynamic aspects. Comparing T_K with the temperature values obtained from the two evaluation models we can classify the quaternary metallic glass Zr₆₅Al_7.5Cu_17.5Ni₁₀, to behave more like a “strong” glass former. Received: 23 January 1998 / Received in final form and Accepted: 31 August 1998     

Specific heat of smoky quartz

Specific heat measurements of smoky quartz are reported between 20 mK and 10 K. The linear temperature dependence observed below 1 K can be attributed to the widely distributed manifold of low-lying energy levels associated with a hole trapped at one oxygen near a substitutional aluminium impurity.     

Specific heat of graphene nanoribbons

We studied the specific heat of graphene nanoribbons (GNRs) using an extended force constant model. We found that at low temperature, the specific heat decreases, and its variation with temperature increases with increasing GNR width. However, the specific heat increases with increasing GNR width after crossing a chaotic region. Free boundary conditions, -CHOH-terminated and armchair-edge-induced phonon nondegeneracy, shift and distortion and localized vibrational modes significantly influence GNR specific heat compared with periodic boundary conditions and bare and zigzag edges in GNRs. Finally, we found a uniform expression for specific heat vs. width at every temperature except for the chaotic region.     

Specific heat of lead grains

The non-quadratic behaviour of the specific-heat enhancement below 5 K as measured by Novoty, Meincke, and Watson for 22 Å lead particles [Phys. Rev. Lett.28, 901 (1972)] is explained by rigorously summing the contributions of all the 183 vibrational modes of the respective free sphere problem. In addition a maximum of the enhancement is predicted near 8 K. The usual asymptotic surface term fails. The mean squared frequency 〈ω²〉 is calculated.     

Specific heat jump in BCS superconductors

An exact analytical expression for the specific heat jump at the critical temperature T_c has been obtained directly from the BCS gap equation for any shape of the energy dependent electronic density of states (DOS). We consider a model which takes into consideration electron-electron repulsion, formulated in the Hubbard model along with the electron-electron attraction due to electron-phonon interaction in the BCS formalism. We have analyzed this expression for constant as well as for the Lorentzian forms of DOS. It is shown that the constant DOS in the simple BCS theory cannot explain the large values of , found in some superconductors. The specific heat versus temperature curve has been found to have a peak, similar to that of Eliashberg theory of superconductivity. The influence of repulsive interaction is very small and occurs mainly at higher temperatures. Received: 26 January 1998     

Specific heat of phenolic polymer

The specific heat of a resole-type phenolic polymer has been determined. A secondary transition is noted at 125° C. The thermodynamic Gruneisen parameter is 1.3 and the lattice Gruneisen parameter is 6.3. Interchain specific heat is about 21% of the total.